Surgical fastening instruments carry a number of surgical fasteners which are typically placed to ligate a vessel, hemostatically staple and cut tissue, or to attach a prosthetic to tissue. All of these instruments contain a plurality of fasteners, which can be placed in a single firing, or in multiple firings. Single firing instruments, such as endocutters or various stapling instruments, contain a plurality of fasteners that are placed within tissue in a single firing. Multifire instruments, such as clip appliers and hernia tackers, contain a plurality of fasteners that are held within the surgical instrument, and the fasteners can be applied one at a time. These types of instruments can be fired repeatedly until the instrument runs out of fasteners or the surgery is complete.
One well known multifire instrument is a clip applier such as the ER320 LIGACLIP™ Multiple Clip Applier manufactured and sold by Ethicon EndoEND-Surgery, Cincinnati, Ohio. Clip appliers are used to close or ligate vessels during surgery, and are commonly used to ligate the cystic duct and cystic artery during the removal of a gall bladder. These surgical instruments can contain up to twenty clips and contain a feed shoe that pushes or feeds the clips distally within the instrument. In particular, a cam tube is advanced over jaws formed on the distal end of the device, thereby camming the jaws closed and crushing a clip disposed between. Some devices also simultaneously retract a feed bar while the cam tube is being advanced to reposition the feed bar in a position to advance the next clip. Once the clip is fully formed, the cam tube is retracted thereby releasing a return spring which is coupled to and advances the feed bar to advance the next clip into the jaws. Similar instruments can be used to deliver a hernia tack or skin staple.
One of the challenges with multifire devices is that a small stroke is repeatedly fired. The stroke must be controlled to allow for rapid repeat firing. Current mechanisms utilize mechanical linkages to accomplish this, however such linkages can be difficult to use in devices having a flexible shaft. In particular, the transfer of force from a handle to an end effector of a device having a flexible shaft can interfere with the tortuous orientation of the shaft, potentially causing it to straighten.
Accordingly, there remains a need for methods and devices for actuating surgical fastening instruments, such as clip appliers, hernia tackers, and skin staplers, and in particular for methods and devices that require a low force to effect actuation.